The present invention relates to a network interworking device to be connected between an IP (Internet Protocol) network in which signal are transmitted in a form of IP packets and an ATM (Asynchronous Transfer Mode) network in which signals are transmitted in a form of ATM cells.
Such a network interworking device called as gateway is typically utilized in for example in internet telephone system, and converts an IP packet used in the IP network into ATM cells used in the ATM network and vice versa.
In the conventional internet interworking device, data conversion has been executed at the highest of the respective protocols. In other words, assembling of ATM cells and disassembling of IP packet have been carried out at user data level.
Such data conversion at the highest layers may result excess overhead or waste because all data conversion processes are not necessary to do at the highest layers.
For example, when audio coding data is transferred, since the audio coding standard is defined uniquely in each network, the audio data received from the ATM network is decoded into pulse code modulation data at the highest layer, and then the decoded data is coded into the audio data to be transmitted to the IP network. Accordingly, wasteful processes are executed when the audio coding standard is the same in both networks. Furthermore, the audio quality will deteriorate at each time the data passes through the network interworking device.
It is therefore an object of the present invention to provide a network interworking device to be connected between an IP network and an ATM network, whereby excess overhead in conversion between an IP packet and ATM cells can be decreased.
According to the present invention, a network interworking device for executing conversion between IP packets and ATM cells comprises, means for assembling a plurality of ATM cells in the ALL layer of said second comunication network into an IP packet when the plurality of the ATM cells are to be transmitted to the same address in said first communication network, said assembled IP packet being transmitted to said IP layer, and means for disassembling an IP packet in the IP layer of said first communication network into a plurality of ATM cells, said disassembled ATM cells being transmitted to said AAL layer.
It is also preferred that each of said ATM cells is an ATM short cell, and wherein an IP address of said IP packet corresponds to a channel identifier CID of said ATM short cell.
It is also preferred that the AAL layer is an AAL type-2 layer.
It is also preferred that when audio coding data is transferred, said audio coding data is converted between an IP packet and ATM cells with each other, without converting via the pulse coded modulation.
Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.